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International Standard Atmosphere
International Standard Atmosphere n (Aeronautics) a theoretical vertical distribution of the physical properties of the atmosphere up to an altitude of 50 km established by international agreement. It permits the standardization of aircraft instruments and performance of all types of flying vehicles international standard atmosphere
international standard atmosphere (ISA) Atmosphere in which the sea level pressure is 1013.25 hectopascals, temperature is 15°C, air density is 0.002378 slugs/ft3 or 1.225 kg/m3, acceleration due to gravity is 32.174 ft/s2 (9.809 m/s2), and the speed of sound is 761 mph, or 1116.4 ft/s (1225.35 km/h). It has a uniform lapse rate until the temperature drops to −56.5°C, at 36,090 ft (11 km), after which the temperature is constant until tropopause. All aerodynamic calculations are based on the ISA. See also ICAN atmosphere.AcronymsSeeISA |